Facilitation of phosphorus uptake in maize plants by mycorrhizosphere bacteria

Abstract

A major challenge for agriculture is to provide sufficient plant nutrients such as phosphorus (P) to meet the global food demand. The sufficiency of P is a concern because of it's essential role in plant growth, the finite availability of P-rock for fertilizer production and the poor plant availability of soil P. This study investigated whether biofertilizers and bioenhancers, such as arbuscular mycorrhizal fungi (AMF) and their associated bacteria could enhance growth and P uptake in maize. Plants were grown with or without mycorrhizas in compartmented pots with radioactive P tracers and were inoculated with each of 10 selected bacteria isolated from AMF spores. Root colonization by AMF produced large plant growth responses, while seven bacterial strains further facilitated root growth and P uptake by promoting the development of AMF extraradical mycelium. Among the tested strains, Streptomyces sp. W94 produced the largest increases in uptake and translocation of ³³P, while Streptomyces sp. W77 highly enhanced hyphal length specific uptake of ³³P. The positive relationship between AMF-mediated P absorption and shoot P content was significantly influenced by the bacteria inoculants and such results emphasize the potential importance of managing both AMF and their microbiota for improving P acquisition by crops.

Figure 1

Time course of radioactivity (³²P, counts per second) monitored in the shoots of Zea mays L. genotype Oh43 inoculated (red squares) or not (blue circles) with Rhizophagus irregularis alone or in combination with different bacterial strains, in Exp. 1. TSA3: Sinorhizobium meliloti TSA3; TSA41: Sinorhizobium meliloti TSA41; CH19: Lysinibacillus fusiformis CH19. Bars represent standard errors.

Figure 2

Linear relationship between shoot dry weight and shoot P content of mycorrhizal (AM) and non mycorrhizal (NM) Z. mays L. genotype Oh43 inoculated with different bacterial strains. Results of the regression analysis are as follows: Exp. 1, NM y = 0.542x + 0.796, R² = 0.631; AMF y = 0.768x − 2.106, R² = 0.609; Exp. 2, NM, y = 0.678x + 0.111, R² = 0.835; AMF y = 0.619x + 0.851, R² = 0.483. For abbreviations see Table 1.

Figure 3

Linear relationship between total ³²P/³³P and total P content of mycorrhizal Z. mays L. genotype Oh43 inoculated with R. irregularis in combination with different bacterial strains. Result of the regression analysis is as follows: Exp. 1, y = 0.077x + 5.748, R² = 0.535; Exp. 2, y = 0.085x + 6.831, R² = 0.303. For abbreviations see Table 1.